Ni II Complexes

We are the first group to succeed with the highly enantioselective 1,3-dipolar cycloadditions of nitronates [75]. Thus, the reaction of 5,6-dihydro-4H-l,2-oxazine N-oxide as a cyclic nitronate to 3-acryloyl-2-oxazilidinone, at -40 °C in dichloro-methane in the presence of MS 4 A and l ,J -DBFOX/Ph-Ni(II) complexes, gave a diastereomeric mixture of perhydroisoxazolo[2,3-fe][l,2]oxazines as the ring-fused isoxazolidines in high yields. The J ,J -DBFOX/Ph aqua complex prepared from... 

Transition metal complexes that are easy to handle and store are usually used for the reaction. The catalytically active species such as Pd(0) and Ni(0) can be generated in situ to enter the reaction cycle. The oxidative addition of aryl-alkenyl halides can occur to these species to generate Pd(II) or Ni(II) complexes. The relative reactivity for aryl-alkenyl halides is RI > ROTf > RBr > RC1 (R = aryl-alkenyl group). Electron-deficient substrates undergo oxidative addition more readily than those electron-rich ones because this step involves the oxidation of the metal and reduction of the organic aryl-alkenyl halides. Usually... 

It is probable that during hydrosilylations these Ni(II) complexes are reduced to 7r-olefin Ni(0) species which then undergo an oxidative addition in an identical manner to that already discussed for the chloroplatinic acid case. There is current interest in such oxidations (83), and the platinum analog (Ph3P)2Pt(olefin) has been shown in one case (olefin = C2H4) to be an excellent hydrosilylation catalyst (240). In this system, intermediate low oxidation state Pt species have been isolated their nature is dependent on the electronegativity of the other groups attached to silicon. 

Two-dimensional protein layer orientation could be also effected by metal-ion coordination Monolayer of iminodiacetate-Cu(II) lipid was successfully employed as substrate for oriented immobilization of proteins naturally displaying histidine residues on their surface [37]. Affmity-resin-displaying Ni(II) complexes could also be successfully employed for oriented protein immobilization [38]. 

Olefin dimerisation with Ni-NHC complexes became a topic of interest following reports of Ni(II) phosphine complexes being employed in imidazolium-based ionic liquid solvents [23, 24]. It had previonsly been established that aIkyl-Ni(II) complexes containing NHC ligands can rapidly decompose via imidazolium formation (Scheme 4.1) [5], and it was thus of interest to explore the effect that an excess of the imidazolinm cation would have on this reaction. 

The remainder of the work on Ni(II) complexes involves the use of chelating ligands in which the carbene is functionalised with pendant heteroatom donor(s). The picolyl-functionalised NHC dicationic complex 29 (Fig. 4.11) was tested for ethylene polymerisation after treatment with MAO [34]. This complex was found to be highly active in a preliminary test (330 kg moF bar h" ), giving predominantly linear polyethylene. Unfortunately this work does not seem to have been followed up. The same system was active for norbomene polymerisation (TOF = 24 400 h" over 1 h). Maximum activity was achieved at 80°C whereafter thermal deactivation became significant, although the nature of this deactivation was not studied. The phenoxide-functionalised carbene complex 30 (Fig. 4.11) was also... 

A series of paramagnetic [NiL-2H] complexes have been isolated in which L = 2,6-diacetylpyridine bis(azacyclothiosemicarbazones) with Ni(II) assuming a distorted five-coordinate structure with d-d bands at about 7250, 10510, 12500, 14400, 19200 and 20500 cm [153], None of these Ni(II) complexes were reported to have activity against the P388 lymphocytic leukemia test system in mice. 

The dependency of 2 on oxidation and reduction of tris(dithiocarbamato) and bis(dithiocarbamato) complexes is illustrated in Fig. 10. The great stability of the andd compounds viz. Cr(R2 c)3 and Co(R2tiic)3 both to oxidation and reduction is remarkable. A similar trend is present in recently published data 191) of the bipy complexes M(bipy)3, M(bipy)3 and M(bipy)3. Maxima in redox stability are found for M = Fe(II), Cr(0) and V(— 1), respectively, which all have configuration. For the few bis(dithiocarbamato) complexes known, the stability of the Ni(II) complexes is greater than for the d Cu(II) complexes. 

Tinnemans et al.132 have examined the photo(electro)chemical and electrochemical reduction of C02 using some tetraazamacrocyclic Co(II) and Ni(II) complexes as catalysts. CO and H2 were the products. Pearce and Pletcher133 have investigated the mechanism of the reduction of C02 in acetonitrile-water mixtures by using square planar complexes of nickel and cobalt with macrocyclic ligands in solution as catalysts. CO was the reduction product with no significant amounts of either formic or oxalic acids... 

Ogura et a/.153 reduced C02 to methanol using the so-called Everitt s salt (K2Fe2+[Fe2+(CN)6])-modified electrode by a somewhat complicated but interesting route in the presence of a metal complex, such as Fe(II), Co(II), and Ni(II) complexes of 1-nitroso-2-naphthyl-3,6-disulfonic acid, and additional methanol ... 

According to Scheme 1, the resulting phosphine-stabilized silylene nickel complex 11 is transformed to the planar Ni(II) complex 12, releasing unstable silylenes (other fragments than Me2Si also can be obtained similarity). Thus complexes like 11 may be regarded as a depot form for silylenes. 

Fox et al.101-103 have studied the structure of Ni(II) complexes being derivatives of frans-l,2-diaminocyclohexane, using 1H NMR spectroscopy. Chemical shift differences (A<5) between di-Schiff base and its nickel (II) complexes observed for aromatic protons were attributed to the ring currents [40]. 

The NMR studies of di-Schiff bases Ni(II) complexes, derivatives (IR,2R)-l,2-diaminocyclohexane and 3- or 5-methoxysalicylaldehyde have been also presented by Szlyk et al.97... 

Scheme 3 refers to oxidative addition of organic halides or derivatives thereof to zero-valent nickel, and to replacement reactions on Ni(II) complexes. 

Kumada and his co-workers (33) later showed that a chiral Ni(II) complex induced asymmetric hydrosilation of a-methylstyrene by meth-yldichlorosilane at 90°C for 60 hours. By use of the trans-(R) isomer of (PhCH2—PhMeP )2NiCl2, they isolated 8% PhMeC HCH2SiMeClH with [a]D + 6.43°and 31% PhMeC HCH2SiMeCl2 with [a] > + 6.50°. The latter compound was treated with methyllithium to prepare PhMeC HCH2SiMe3, [a], + 10°, which they estimated as 17.6% optically pure. 

Large negative AS values for redistribution and replacement reactions of planar Ni(II) complexes of N-alkyl-a-aminoxime ligands ... 

Formation and dissociation kinetics of nine Ni(II)-macrocyclic tetra-thiaether complexes (eight macrocyclic, one linear in acetonitrile) have been compared with those for Cu(II) analogues and for Ni(II) complexes with macrocylic tetramines (262). Whereas for the tetramine complexes conformational changes may be apparent in the kinetics this is not the case for the tetrathiaether complexes, where there is no kinetic evidence for slow conformational changes after initial bonding of the ligand to... 

The Ni(II) complexes 6 and 7 have been found by Stiles [60] to be soluble catalysts for reductive dehalogenation when combined with NaBH4 or hydrazine at 25-45 °C in protic solvents. Reactivity toward the reducing system increased with the halogen content of the substrate. Aryl bromides were converted much faster than chlorides, polychlorobenzenes, however, reacted readily with stepwise loss of chlorine. 

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